1. Field of the Invention
This invention relates to a method of selectively depositing a metal on a surface of a substrate and more particularly, to depositing a metal pattern on a nonconductive substrate utilizing a method comprising a selective exposure to a source of ultraviolet radiation.
2. Description of the Prior Art
There is a growing need in various device and circuit applications for an inexpensive process which will produce adherent conducting circuit patterns on a nonconductive surface. Most of the processes used for metallic pattern generation involve a photographic step. Pattern resolution may be good but most methods are often slow, involving many process steps, and are relatively expensive.
A conventional method for producing macro circuit patterns employs a copper-clad insulator board coated with a photoresist material which is photoexposed and chemically processed to selectively remove copper, leaving a desired circuit pattern. This method is effective but wasteful of copper and chemicals.
An electroless metal deposition process is especially attractive for metallic pattern generation since one only needs to produce a pattern of a suitable catalyst on a substrate and metal deposition will occur only on that pattern. Generally speaking, a conventional electroless plating process includes sensitizing an electrically non-conducting surface with a sensitizer, e.g., a stannous chloride solution. The surface is then immersed in an activating solution, comprising an activating metal salt, e.g., a noble metal salt, wherein an activating metal is reduced on the surface. The activating metal-reduced surface is then subjected to an electroless metal deposition bath, which is catalyzed by the reduced activating metal, and wherein an electroless metal deposit is obtained.
A refinement of the conventional electroless plating process is necessary when the electrolessly plated metal is electrolessly deposited onto selected portions of a substrate surface in a pattern rather than on the entire surface, to produce a printed circuit board. One such process is disclosed in U.S. patent application Ser. No. 814,564, filed by M. A DeAngelo on July 11, 1977 and now U.S. Pat. No. 4,096,843, and entitled "A Method of Selectively Deposition a Metal on a Surface of a Substrate," and assigned to the assignee hereof, wherein a hydrazine and/or substituted hydrazine-treated surface is selectively exposed to a source of ultraviolet radiation to delineate an ultraviolet radiation-exposed pattern no longer capable of desensitizing an electroless metal deposition sensitizer, such as Sn.sup.+2 ions. The ultraviolet radiation exposed surface is then treated with a sensitizer, followed by treatment with an activator to form a catalytic activating metal pattern which can be electrolessly metal deposited.